It is known to use so-called broad-slit or wide-mouth dies for the extrusion of thermoplastic synthetic resins in the formation of relatively thin and relatively wide workpieces or extrusions and, in the case in which a multilayer foil or plate is desired, to connect two or more extruders to the die so that the respective flow passages merge at the die orifice or lip which is relatively narrow and elongated to extrude the flat thin workpiece.
Between the inlets from the extruders on the die and the elongated orifice, spreading channels can be provided so that the thermoplastic synthetic resin flow can spread out and uniformly reach the die orifice or lip.
Usually the extruders are connected by respective fittings to the inlets, these fittings having axes. The individual layers of the thermoplastic synthetic resin forming the extrusion can be constituted from the same plastic material which can be modified from one layer to the other or not, e.g. by foaming one of the layers, or from different synthetic resins.
Generally all of the axes of the inlet orifices are located in a longitudinal median plane and thus at a midpoint of the extrusion die, one above another. The extrusion die is generally fabricated from a number of parts and, because of the location of the fittings, assembly may be complex or the die may have to be of very complicated construction.
Since all of the inlet fittings are customarily located at the front side of the die block opposite the die outlet orifice, it is rather complex to connect the extruder units to the fittings. Worm-type extrusion presses are relatively long and massive and would tend to interfere with one another if they were connected directly to the fittings. Accordingly, it was customary to connect the extruders by long pipelines which may have bends or the like in them. This, of course, is a costly construction, makes cleaning and maintenance difficult and expensive and requires heating of long stretches of pipe. It will be understood that most of the paths of the thermoplastic, until the extrusion emerges from the dies, require heating.
It is not possible, therefore, with earlier constructions as described, to directly connect the extrusion presses to the die.